Electric heater for tumble dryers

ABSTRACT

The electric heater for tumble dryer devices, object of the present invention, does not need the large size presently required to provide high powers. Furthermore, the particular shape of the resistive member reduces the vibrations transmitted to the apparatus and therefore the noise felt by the user. The particular shape of the heater determines a lower tendency to dust deposition on the heating member and a higher safety against short circuits in case of filament breakage.

RELATED APPLICATION

This application claims priority to Italian Patent Application No. RM2008A000516, in the name of I.R.C.A. S.p.A. Industria Resistenze Corazzate E Affini, filed on Sep. 30, 2008.

FIELD OF THE INVENTION

The present invention relates to an electric heater used in tumble dryer devices.

STATE OF THE ART

Various electric heaters used in tumble dryer devices are known.

Some known electric heaters have at least a coil-shaped wire, for example helically wound, which is fitted on a support structure.

While such electric heaters with coil-shaped wire are commonly used in the tumble dryer devices, they have some disadvantages.

A first disadvantage is that large heaters are needed in order to provide a sufficient heating power, e.g. higher than 5 kW.

A second disadvantage is that the air flow passing through the coil-shaped wires may cause vibrations in the wires, and therefore an irritating noise during operation.

A further disadvantage is due to the coil-shaped heating wires tending to become curved and capture dust, and their breakage may cause short circuits.

It is therefore felt a need for implementing an electric heater for tumble dryers which allows to overcome the aforesaid drawbacks.

SUMMARY OF THE INVENTION

The primary object of the invention is to implement an electric heater for tumble dryers which allows to simply and functionally overcome the aforementioned drawbacks. Such a heater is provided with a compact structure consisting of at least one resistive member having a zigzag-bent, “flattened wire” section, supported by a multilayer structure made of an insulating material.

Another object of the invention is to implement an electric heater which simplifies the application to the used apparatus while ensuring a high safety level.

Therefore, the present invention aims at attaining the above-discussed objects by implementing an electrical heater for tumble dryer devices which, in accordance with claim 1, comprises at least one resistive member, a support structure for supporting said at least one resistive member, in which said support structure comprises flat parts which are connected to one another so as to define a polygonal shape of the structure having at least one open side, and in which said at least one resistive member comprises a flattened filament which is bent so as to define a plurality of zigzags, said filament being arranged on a plane which is substantially perpendicular to each flat part of the support structure.

Each flat part or strip is formed by three overlaying layers of an insulating material and is provided, at one longitudinal edge thereof, with a substantially L-shaped support member having a short arm connected to the flat part and a long arm adapted to be connected to a heater housing, so that the flat parts are arranged along plans which are orthogonal to the bottom of said housing.

Each flat part and the respective support member may be integrally secured to one another or constructed as a single piece. Alternatively, there is provided a single support member with flat parts or strips of the support structure secured thereto.

The heater object of the present invention does not advantageously require the large size presently needed to provide high powers. Furthermore, the particular shape of the resistive member reduces the vibrations transmitted to the apparatus and therefore the noise heard by the user. A further advantage given by the heater shape is the lower tendency to dust deposition on the heating member and the safety against short circuits in case of filament breakage.

A variant of the invention provides for the possibility of inserting more resistive members so as to be able to choke the total power with a subsequent energy saving in case of not full loads of laundry in the dryer.

A further variant provides for the possibility of placing the resistive members on the optimal side, e.g. either on the inner side only or on the outer side only or on both sides, with respect to the polygonal structure formed by the mica supports of the heater, by adjusting the heater itself to the specific requirements of the apparatus. A first variant, for example, provides for a single resistive member arranged outside or inside the support structure. On the other hand, a second variant provides for a first resistive member arranged outside the support structure and at least one a second resistive member arranged inside said support structure. In a preferred variant, there are provided two second resistive members arranged inside the support structure. Alternatively, there may also be provided two resistive members arranged outside the support structure and one resistive member inside.

Other variants may be obtained by providing for the possibility of varying the final geometry of the heater by using a single support structure with the advantage of being able to use the same resistor on variously sized apparatuses, thus avoiding costs for specific equipment.

The dependent claims describe preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will be more apparent in view of the detailed description of a preferred not exclusive embodiment of an electric heater, illustrated by way of non-limiting example, with the aid of the accompanying drawings, in which:

FIG. 1 shows a view of an electric heater according to the invention;

FIG. 2 shows a cross-section view of the heater in FIG. 1;

FIG. 3 shows an exploded view of part of the heater in FIG. 1;

FIG. 4 shows a partially exploded view of part of the heater in FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

With reference to the Figures, a first preferred embodiment of an electric heater is depicted, globally indicated by reference numeral 1, which may be especially used in tumble dryer devices.

In this first embodiment, the heater object of the present invention comprises:

at least one resistive member, or simply resistor, 8 arranged on an outer side of the heater;

at least two resistive members 9 arranged on an inner side of the heater;

a support structure 6 for said resistive members 8 and 9 having a polygonal shape with at least one open side;

means 3 for connecting resistive members 8 and 9 to the mains for powering the resistors.

By passing forced air, e.g. at a rate higher than 5 m/s, through the resistors having a design temperature at a steady state of e.g. 400° C., the air rapidly heats thus allowing the laundry placed in the household appliance compartment to be dried.

Support structure 6 advantageously comprises a plurality of strips or flat parts 6′ made of an insulating material, having high dielectric strength and excellent chemical stability, preferably mica. Other usable insulating materials may be ceramic materials such as steatite or cordierites.

Strips 6′ are reciprocally connected at their ends so as to form a polygonal-shaped structure with at least one open side. Strips 6′ are at least four in number.

Therefore, support structure 6 has two ends 10, 11 spaced apart by an empty spacing or gap 12. These ends 10, 11 are provided with electric terminals 4 for the connection to the electric network.

In the preferred embodiment of FIG. 1, strips 6′ are seven in number.

Each strip 6′ is formed by three layers 13, 14 and 15 of mica or other suitable insulating material and is integrally secured, at the longitudinal edge thereof, to a substantially L-shaped support member 7, which may be better seen in FIG. 2. The short arm of this L-shaped member is secured to strip 6′, whereas the long arm is secured to the housing 5 of the heater so that strips 6′ are arranged along plans which are orthogonal to the bottom of housing 5.

In an alternative variant, each strip 6′ and the respective L-shaped support member 7 may be constructed as a single piece.

In a further variant, there is provided a single support member to which all strips 6′ of the support structure are secured. This single support member is suitable for being connected to the housing 5 of the heater so that strips 6′ are arranged along plans which are orthogonal to the bottom of said housing 5.

With reference to FIGS. 3 and 4, the outer mica layer 13 of each strip 6′ of support structure 6 is advantageously provided with a first longitudinal series of holes 16, substantially arranged along the longitudinal axis of the strip, within which a first resistor 8 is passed, the resistor being defined by a zigzag-shaped, flattened filament and secured between said outer layer 13 and the intermediate mica layer 14.

On the other hand, the inner mica layer 15 of each strip 6′ is provided with two second longitudinal series of holes 17, 18 arranged along straight lines parallel to one another and to the longitudinal axis of the strip, close to said axis. A respective second resistor 9 is passed within each second series of holes, the resistor being defined by a zigzag-shaped, flattened filament and secured between said inner layer 15 and the intermediate mica layer 14.

Alternatively, in a second preferred embodiment, a single series of holes and therefore a single resistor 9 may also be provided on the inner mica layer 15.

The zigzag shape of the resistors or heating filaments 8, 9 has first tips which are connected to support structure 6 and second tips which are spaced apart from said support structure. By securing the first tips of the resistors to the support structure by means of the holes provided on the inner and outer mica layers 15, 13, short circuits and bending of resistors are avoided even in case of filament breakage. The arrangement of the resistors allows a high strength also against intense air flows, only minimal vibrations being produced.

The three mica layers 13, 14, 15 are held by means of rivets or other suitable securing means so as to be integral with one another. The mica layers provide electric insulation and prevent the resistors from coming in contact with one another or with parts of the household appliance once the heater of the invention has been installed.

This configuration of resistors 8 and 9, arranged on planes which are substantially perpendicular to strips 6′ and substantially parallel to the bottom of housing 5, advantageously allows to offer the lowest resistance to the air flow, thus optimizing the thermal yield and the load loss.

Specifically, providing in the first embodiment two resistors 9 on the inner side of the heater is advantageous because, even in cases with less ventilation in the central zone of the apparatus, the surface temperature of the resistive filament may be limited by doubling the heat emitting surface.

Resistors 8, 9 are at least 10 mm wide, preferably from 20 and 30 mm wide. They are made of materials such as, for example, resistive FeCrAl—FeNiCr alloys.

The distance between the series of holes 17, 18 related to the side having more filaments is at least 6 mm, preferably between 7 and 20 mm.

A further advantageous embodiment of the invention provides for a single resistor or resistive member or filament, having a “flattened wire”, zigzag-bent section, placed on the inner or outer side of the heater.

The turn “connecting” two sectors of the mica supports or strips 6′ which define the support structure 6, is inserted into an appropriate “open” slit so that the shape of the turn itself may automatically conform to the configuration produced by the support structure 6.

This is effective both on the inner side of the polygon formed by the strips 6′ where there is provided at least a slit 20 open at the ends of the inner mica layers 15, and on the outer side of said polygon where there is provided at least a slit 19 open at the ends of the outer mica layers 13. The corresponding open slits in the inner and/or outer layers are suitable for defining a passage for a turn of a resistive member between two subsequent flat parts or strips 6′.

This peculiarity, along with the possibility of taking different sizes for anchoring the heater to the apparatus, allows to make the same resistor also applicable to apparatuses which are dimensionally different to one another. Indeed, by varying the angle defined by the connection between strips 6′, the median diameter taken by the resistor varies, i.e. the aforesaid diameter increases with the increase in the angle, thus allowing to obtain different sizes for anchoring the heater to the tumble dryer device. 

1. An electric heater for tumble dryer devices, comprising at least one resistive member, a support structure for supporting said at least one resistive member, wherein said support structure comprises flat parts, which are connected to one another so as to define a polygonal shape of the structure, having at least one open side, and wherein said at least one resistive member comprises a flattened filament which is bent so as to define a plurality of zigzags, said filament being arranged on a plane which is substantially perpendicular to each flat part of the support structure.
 2. A heater according to claim 1, wherein each flat part is formed by three overlaying layers of an insulating material.
 3. A heater according to claim 2, wherein each flat part is provided, at one longitudinal edge thereof, with a substantially L-shaped support member, having a short arm connected to the flat part and a long arm adapted to be connected to a housing of the heater, so that flat parts are arranged along plans which are orthogonal to the bottom of said housing.
 4. A heater according to claim 2, wherein all flat parts are secured to a single support member adapted to be connected to a housing of the heater, so that the flat parts are arranged along plans which are orthogonal to the bottom of said housing.
 5. A heater according to claim 1, wherein said at least one resistive member is arranged outside or inside the support structure.
 6. A heater according to claim 1, wherein there are provided one first resistive member arranged outside the support structure and at least one second resistive member arranged inside said support structure.
 7. A heater according to claim 2, wherein said at least one resistive member is arranged outside or inside the support structure.
 8. A heater according to claim 2, wherein there are provided one first resistive member arranged outside the support structure and at least one second resistive member arranged inside said support structure.
 9. A heater according to claim 8, wherein there are provided two second resistive members (9) arranged inside the support structure.
 10. A heater according to claim 7, wherein an outer layer or an inner layer of each flat part are provided with a first longitudinal series of holes within which first tips of said at least one resistive member are secured.
 11. A heater according to claim 8, wherein an outer layer is provided with a first longitudinal series of holes within which first tips of said first resistive member are secured, and wherein an inner layer is provided with at least a second longitudinal series of holes within which first tips of said at least one second resistive member are secured.
 12. A heater according to claim 2, wherein there is provided at least a slit open at the ends of the inner layers of each flat part and/or at least a slit open at the ends of the outer layers of each flat part suitable for defining a passage for a turn of said at least one resistive member between two subsequent flat parts. 